White inks

Abstract

The present disclosure provides a white ink including an aqueous ink vehicle; from 5 wt % to 50 wt % of a white metal oxide pigment having an average particulate size from 75 nm to 2,000 nm and a refractive index of 1.8 to 2.8; and from 0.1 wt % to 15 wt % of fumed oxide particulates having a tertiary agglomerated average particulate size from 20 nm to 750 nm and a refractive index of 1.1 to 1.6. The white ink further includes a polymeric dispersant associated with a surface of the white metal oxide pigment.

What is claimed is: 
     
       1. A white ink, comprising:
 an aqueous ink vehicle; 
 from 5 wt % to 50 wt % of a white metal oxide pigment having an average particulate size from 75 nm to 2,000 nm and a refractive index ranging from 1.8 to 3.0; 
 from 0.1 wt % to 15 wt % of fumed oxide particulates having a tertiary agglomerated average particulate size from 20 nm to 750 nm and a refractive index of 1.1 to 1.6; and 
 a hydrophilic polymeric dispersant coating on a surface of the white metal oxide pigment. 
 
     
     
       2. The white ink of  claim 1 , wherein the white metal oxide pigment and fumed oxide particulates are present in the white ink at weight ratio from 2:1 to 50:1. 
     
     
       3. The white ink of  claim 1 , wherein the white metal oxide pigment includes titanium dioxide particulates, zinc oxide particulates, zirconium oxide particulates, or combinations thereof. 
     
     
       4. The white ink of  claim 1 , wherein the fumed oxide particulates include fumed semi-metal oxide particulates. 
     
     
       5. The white ink of  claim 1 , further comprising from 2 wt % to 30 wt % latex particulates having a glass transition temperature from −20° C. to 130° C., and wherein white metal oxide pigment and latex particulates are present in the white ink at a weight ratio from 6:1 to 1:3. 
     
     
       6. The white ink of  claim 5 , wherein the white metal oxide pigment has an average particle size from 170 nm to 400 nm, and the average optical spacing between white metal oxide pigment particles when the white ink is printed and fused is from 30 nm to 300 nm resulting in a fused image having a normalized opacity from 45% to 95%. 
     
     
       7. The white ink of  claim 5 , wherein the white ink printed on a non-porous substrate at ink coating density 30 gsm and heat fused at 10° C. above minimum film formation temperature of the latex particles has an opacity L* improvement of at least 5% greater than a comparative ink printed and heated under the same conditions, wherein the comparative ink is devoid of the fumed oxide particulates and replaced by ink vehicle. 
     
     
       8. The white ink of  claim 1 , wherein the polymeric dispersant includes a short-chain anionic dispersant having an acid number higher than 100 mg KOH/g based on dry polymer weight, or a non-ionic or predominantly non-ionic dispersant having an acid number not higher than 100 mg KOH/g based on dry polymer weight. 
     
     
       9. The white ink of  claim 8 , wherein the polymeric dispersant comprises both the short-chain anionic dispersant and the non-ionic or predominantly non-ionic dispersant, and wherein the polymeric dispersant is co-milled with the white metal oxide pigment, thereby modifying both particles of the white metal oxide pigment and the surface thereof with the polymeric dispersant. 
     
     
       10. The white ink of  claim 1 , wherein the white ink is a thermal inkjet ink. 
     
     
       11. A method of making the white ink of  claim 1 , comprising:
 milling the while metal oxide pigment in a water-based carrier with the hydrophilic polymeric dispersant to form a white metal oxide pigment dispersion; and 
 admixing water, organic co-solvent, and the fumed oxide particulates with the white metal oxide pigment dispersion to form the white ink. 
 
     
     
       12. The method of  claim 11 , further comprising admixing latex particulates into the white ink, and wherein the white ink comprises:
 from 5 wt % to 50 wt % of the white metal oxide pigment having an average particulate size from 100 nm to 1,000 nm; 
 from 0.1 wt % to 15 wt % of the fumed oxide particulates having a tertiary agglomerated average particulate size from 30 nm to 500 nm; and 
 from 2 wt % to 30 wt % of the latex particulates having a glass transition temperature from 0° C. to 130° C. 
 
     
     
       13. A fluid set for inkjet imaging, comprising:
 the white ink of  claim 1 ; and 
 a fixer fluid, comprising:
 aqueous fixer vehicle, and 
 from 0.1 wt % to 25 wt % cationic polymer. 
 
 
     
     
       14. The fluid set of  claim 13 , wherein the white ink is formulated for inkjet application, and wherein the fixer fluid is formulated for inkjet application having a viscosity from 1 cP to 35 cP at 25° C. 
     
     
       15. The fluid set of  claim 13 , wherein the white ink is formulated for inkjet application, and wherein the fixer fluid is formulated for analog application having a viscosity from 1 cP to 500 cP at 25° C. 
     
     
       16. The white ink of  claim 1 , wherein the white metal oxide pigment is present in an amount from 25 wt % to 50 wt %. 
     
     
       17. The method of  claim 11 , wherein the hydrophilic polymeric dispersant is a short-chain anionic dispersant, a non-ionic or predominantly non-ionic dispersant, or combination thereof. 
     
     
       18. The method of  claim 11 , wherein the white ink has a white metal oxide pigment to fumed oxide particulate weight ratio from 2:1 to 50:1. 
     
     
       19. The fluid set of  claim 13 , wherein the white metal oxide pigment has an average particulate size from 100 nm to 1,000 am. 
     
     
       20. The fluid set of  claim 13 , wherein the filmed oxide particulates have a tertiary agglomerated average particle size from 30 nm to 500 nm.